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Insulin-like growth factor 1 molecule. Computer model showing the structure of a molecule of the hormone insulin-like growth factor 1 (IGF-1). IGFs are polypeptides that are similar in their molecular structure to insulin. IGF-1 is mainly secreted by the liver as a result of stimulation by growth hormone (GH). In addition to acting in a similar way to insulin, IGF-1 can also regulate cell growth and development, especially in nerve cells, as well as cellular DNA synthesis. It plays an important role in growth and development throughout childhood and into adulthood.